Imagery is presented in many forms. In the classical optical camera, for example, light energy from an object scene is focused through glass optics onto a film formatted image plane where light sensitive film records the scene. Typically, the film format corresponds to xe2x80x9c35 mmxe2x80x9d film, which translates to maximum linear dimensions of 36.3 mm (horizontal) by 24.2 mm (vertical), or a vertical-to-horizontal ratio of 3:2.
In the electronic age, the classical film-formatted camera is being quickly replaced by the solid-state camera utilizing charge coupled devices such as the xe2x80x9cCCDxe2x80x9d array. Typically, the CCD array is formatted to conveniently correlate with the computer display screen, which has a horizontal-to-vertical aspect ratio of 4:3. In this manner, the CCD array and computer display are matched on a pixel-to-pixel basis.
However, regardless of the high quality image presented by the classical film-formatted camera, its optics and housing are unsuitable for application with the CCD array. Accordingly, as users convert to digital cameras, their older film-formatted cameras shall become obsolete. Not only will the typical user have to buy a new camera, i.e., the digital camera, she will discard or retire the film-formatted camera, creating both cost and waste.
It is, accordingly, one object of the invention to provide apparatus and methods for adapting film-formatted cameras to solid state devices such as the CCD array in a compact and useful manner. A corollary object of the invention is to provide reimaging methods to achieve selected magnification and/or demagnification for each of the tangential and sagittal axes.
The prior art is known to have created optical systems for relaying and magnifying or demagnifying optical images by way of an optical system such as a relay lens. Specifically, in the prior art, it is known that a relay lens can be used to relay one image plane to another image plane at a selected magnification (or demagnification) ratio. However, such an arrangement is unwieldy and would generally double the size of the classical camera, making the approach non-practical as a solution to the above-described problem. Further, it is very difficult, and thus costly, to simultaneously provide selected magnifications for both of the tangential and sagittal axes. By way of example, it is known that an astigmatic optical element provides such a bifurcated magnification; however, this element requires additional aspheric processing, adding cost, time and complexity to the manufacturing process.
The problems discussed above are symptomatic of a wide range of display problems and inconveniences experienced today. In the electronic and medical world, for example, imagery is often displayed on a television (TV), a computer display, the liquid crystal display (LCD), the cathode ray tube (CRT), light-emitting diode arrays, and back projection systems. It is often desirable, however, to illustrate the electronic display in a different format such as to a wider audience on a large format display. In the prior art, for example, complex projection systems are sometimes used to relay a smaller electronic display onto a large, reflective surface such as a white wall or a projection screen. However, it is widely understood that projection display systems are large in size, expensive, and heavy; and they inefficiently consume large amounts of electrical power. They are also generally limited to use in darkened areas due to low luminance output and poor efficiency.
An electronic display that is generally defined as a Flat Panel Display (FPD) has other difficulties that are not adequately addressed in the prior art, such as limitations in luminance and angular view. The active matrix thin film transistor liquid crystal display (AM-TFT LCD), the passive LCD, the field emission display (FED), and other FPDs (such as plasma displays and electroluminescent displays) each have characteristic angular fields due to inherent construction, polarizing filters and fore- and back-light characteristics (if required). One example of the angular limitations inherent in a FPD is readily seen in observing a portable computer screen from different angles: the portable FPD is barely visible, if at all, from viewing angles greater than about forty-five degrees from the normal to the screen surface.
The angular and luminance limitations associated with viewing a FPD are thus significant. Most observers prefer to view an image that is highly uniform in luminance over a wide field angle. This further compounds the difficulty in converting the FPD to a large format display. In addition, daylight viewing and the suppression of glare often necessitate additional screens or intermediate optics between the FPD and the observer, adding other costs and complexity. In certain applications, the prior art has attempted, without great success or efficiency, to improve the field of view of the FPD through the addition of diffractive spatial filters placed adjacent to the FPD screen.
There is the need, therefore, of enhancing the performance of the FPD. It is, accordingly, an object of the invention to provide apparatus and methods for enhancing the luminance and field of view of the FPD. A further object of the invention is to provide systems for converting the FPD to a large format display with improved luminance and field of view.
Highly commercial electronic displays have still other difficulties. For example, very large commercial advertising and stadium-sized matrix displays are assembled using tiles of bulbs, CRTs, light emitting diodes (LEDs), or LCD panels. Not only are these systems limited in resolution, color (note, e.g., that LEDs are typically one color) and general optical performance, they are expensive, costing in the neighborhood of $100,000 per square meter. They additionally have low reliability standards and few specifications or limitations on weight, power consumption and efficiency.
It is, accordingly, an object of the invention to provide a system which transforms the image presented by an electronic displayxe2x80x94such as the LCD, the CRT, the FPD, phosphor displays, an array of LEDs, a computer screen, and a pixelated objectxe2x80x94into a reformatted image with enhanced or modified features, such as with selected magnification, astigmatism, distortion, optical correction, optical processing, and Fourier content.
Another object of the invention is to provide apparatus and methods for magnifying or demagnifying an image of an object with a compact and substantially monolithic optical system.
Still another object of the invention is to provide methods of manufacturing and constructing combinations of lenslet arrays to achieve magnification or demagnification selectively.
Yet another object of the invention is to provide optical correlating apparatus and methods for conveniently achieving Fourier processing of an electromagnetic field.
These and other objects will become apparent in the description which follows.
As used herein, xe2x80x9cmagnificationxe2x80x9d is sometimes used to denote both magnification and demagnification. Accordingly, xe2x80x9cmagnificationxe2x80x9d is sometimes used herein to denote a magnification of greater than one, a demagnification of less than one, and unit magnification.
As used herein, a xe2x80x9clenslet arrayxe2x80x9d refers to an array of microlenslets that are arranged into an optical substrate surface. A single lenslet array can therefore include an array of refractive lenslets or an array of non-refractive lenslets. As used herein, xe2x80x9cnon-refractive lensletsxe2x80x9d generally mean diffractive lenslets. However, non-refractive lenslets can include holographic steering lenslets, phase modulating lenslets, and index modulating lenslets (including gradient index modulation formed through ion implantation and ion exchange, and effective index modulation using nanometer cuts within a substrate surface). A lenslet array is formed with an optical surface substrate which is typically planar except for the micro-features of the microlenslets. However, those skilled in the art will appreciate that lenslets arrays can be formed internally to an optical substratexe2x80x94and thus not on the surfacexe2x80x94or onto curved surfaces (e.g., macrolenses) which provide additional optical power.
A xe2x80x9cstackxe2x80x9d as used herein refers to a plurality of lenslet arrays arranged substantially adjacent to one another to operate as a single optical system. Generally, a stack has at least two lenslet arrays forming an array of xe2x80x9clenslet channels,xe2x80x9d each of which has at least one refractive lenslet and at least one non-refractive lenslet. In order to achieve radiation transfer along each lenslet channel, each lenslet array in a stack typically has like numbers of lenslets so that there is a one-to-one correspondence between the lenslets of one channel (that is, each lenslet of each array has a corresponding lenslet in each of the other arrays; the corresponding lenslets forming the channel between the several arrays).
As used herein, a xe2x80x9ctilexe2x80x9d refers to mosaic of like elements to operate, substantially, as a single element. In the typical case, a tile can be formed, for example, by an array of like lenslet array stacks which are abutted, end to end, so as to substantially function as a single stack.
As used herein, a xe2x80x9cstacked array imaging systemxe2x80x9d, or xe2x80x9cSAM,xe2x80x9d refers to an imaging system such as a stack arranged to view and image objects. For example, a SAM can include a magnifying or demagnifying optical system.
As used herein, xe2x80x9cpixelatedxe2x80x9d refers to the quantized nature of certain objects and images. For example, most computer displays are made up of a thousands of pixels emitting light energy at the command of the computer""s central processing unit (CPU). Such a display is xe2x80x9cpixelatedxe2x80x9d since it is quantized. By way of another example, a solid state device such as a CAMCORDER records continuous, real-world imagery via a CCD array; and the data captured by the CAMCORDER is thus pixelated or xe2x80x9cdiscrete.xe2x80x9d High speed computing via fiber-optics and electrical paths can also be xe2x80x9cpixelatedxe2x80x9d in that data, often made up of large digital words, are processed in a massively parallel fashion (sometimes denoted herein as xe2x80x9cmassive parallel processingxe2x80x9d or xe2x80x9cMPPxe2x80x9d). By way of comparison, real world objects like a human being are continuous; and a picture (i.e., an image) taken of real world objects onto film emulsion is also continuous since it is not quantized.
As used herein, a xe2x80x9cMicro Electromechanical Systemxe2x80x9d, or xe2x80x9cMEMSxe2x80x9d, refers to an actuator or electromechanical device or micro miniature machine that is placed between stacks or is constructed onto a stack element. For example, a SAM consisting of a stack of fixed lenslet arrays can have a fixed magnification at a fixed set of imaging conjugates. By building a SAM with an active actuator mechanism or MEMS at an intermediate image plane, then the magnification of the imaging system is adjustable and variable according to an electronic impulse signal to the actuator, thereby changing the spacing between the image forming stacks. By way of comparison, an autofocus camera has a motorized screw mechanism for movement of the optical elements in the camera objective in order to change the focus and/or f-stop of the camera.
In one aspect, the invention provides a stacked array magnifier (SAM) for forming a magnified image of an object. The SAM includes one or more non-refractive lenslet arrays and one or more refractive lenslet arrays to form a plurality of lenslet channels. Each lenslet channel has at least one refractive lenslet and at least one non-refractive lenslet, and the lenslet channels between at least two adjacent arrays are sloped relative to an optical axis between the object and the image. The sloped lenslet channels that are further from the optical axis have larger slopes than the sloped lenslet channels closer to the optical axis. Together, the slopes of the several channels provide selective magnification between the object and the image.
In another aspect, the lenslet arrays form a stack between a first surface facing the object and a second surface facing the image. The lenslet channels extend further from the optical axis at the first surface, and closer to the optical axis at the second surface, thereby providing demagnification of the object at the image. Such an aspect can include a solid state focal plane at the image plane which is substantially perpendicular to the optical axis so as to receive electromagnetic radiation from the object.
In still another aspect, the lenslet arrays form a stack between a first surface facing the object and a second surface facing the image. The lenslet channels extend further from the optical axis at the second surface and closer to the optical axis at the first surface, thereby providing magnification of the object at the image.
In accord with the invention, the lenslet channels typically have clear aperture diameters of between about 5 xcexcm and 1000 xcexcm. As shown herein, certain experimentation was conducted with clear apertures of about 168 xcexcm.
In another aspect, the stack can include a macrolensxe2x80x94i.e., a lens element that is substantially larger than any of the lensletsxe2x80x94that is arranged between at least two adjacent arrays. The macrolens is included, generally, to add optical power between the object and image.
To effect continuous imaging, in another aspect, a plurality of lenslet channels are arranged so as to contribute to each point in the image. In order to provide an erect image, the SAM of this aspect must have 2n+1 internal images, where n is an integer.
Lenslet arrays can be constructed and arranged according to the invention to provide a magnification ratio of less than about 8:1 between the object and the image. A second stacked array magnifier can thus be used, in sequence, to provide secondary magnification of the object to a secondary image along the optical axis. The second SAM is substantially similar to the first SAM, though the magnification need not be the same. In this manner, a magnification from each SAM is multipliedxe2x80x94e.g., 8:1xc3x978:1, which provides an overall magnification of 64:1.
In other aspects, the SAM is transmissive to visible electromagnetic radiation between about 400 nm and 750 nm. As such, a CCD array can be conveniently arranged at the image and substantially perpendicular to the optical axis so as to collect the visible electromagnetic radiation from the object. However, SAMs of the invention can be made to function with any range of wavelengths, such as the ultraviolet and infrared.
For example, the SAM can also be made transmissive to infrared electromagnetic radiation; and can include xe2x80x9cuncooledxe2x80x9d microbolometer arrays or other IR detectors, e.g., HgCdTe, at the focal plane. In another aspect, the lenslet arrays are made transmissive to visible electromagnetic radiation between about 540 nm and 580 nm, which corresponds to certain phosphor display devices in the medical arts. Accordingly, the SAM material is optimized in transmission and diffraction features within the wavelength of interest. Note that the non-refractive lenslets have greater efficiency for a smaller waveband when optimized to that waveband. By way of example, those skilled in the art should appreciate that non-refractive lenslet arrays which include blaze grating features have the best efficiency at the designed wavelength. Blaze gratings can be optimized in angle to provide peak diffraction efficiency, for example, at phosphor emission wavelengths.
To restrict the FOV and to reduce cross-talk, at least one refractive lenslet array of the invention can operate to form an intermediate image of the object and within the SAM. A field stop is then located at the intermediate imagexe2x80x94or very near to the imagexe2x80x94to limit the field of view of one or more lenslet channels. Similarly, a Lyot stop can be located at the intermediate image to reduce cross-talk from out-of-field radiation (preferably, the stop reduces stray light cross-talk to less than about 10% of all of the electromagnetic radiation transmitted from the object and to the image). To be most effective, the stops should be within about a blur distance from the internal SAM image, whereby the defocus wavefront error is less than about xc2xcxcex.
In a preferred aspect of the invention, each lenslet channel includes an array of three lenslets at each lenslet array. These three lenslets are transmissive to a unique RBG color such that substantially any color can be transmitted along each channel. At the same time, each of the non-refractive lenslets are preferably optimized for optical efficiency corresponding to the RBG color associated with its channel.
The invention also provides for interlaced imaging, or for pixelated imaging so as to produce an array of discrete images of the object. In this latter aspect, the FOV of each channel is substantially non-overlapping with adjacent channels to accommodate efficient discrete collection by a solid state sensor.
The lenslet arrays of the invention can also include, in another aspect, one or more optical coatings to improve optical transmission through one or more lenslet channels.
In one aspect, a SAM is constructed and arranged so as to have an overall f-number that is less than any of the lenslet f-numbers. For example, if each of the lenslet channels is constructed and arranged so as have an f-number of f/1 or greater, the overall f-number of the magnifier is less than about f/1.
In yet another aspect, the SAM of the invention can include means for creating diffraction orders of electromagnetic radiation transmitted between the object and the image, the orders being sufficient to provide greater than approximately 90% efficiency. Similar means can also be included to improve the imaging resolution within the image with a modulation transfer function of greater than about 10% at image frequencies greater than about 500 lp/mm.
In certain aspects, lenslets of the invention can include refractive surfaces with aspheric shapes. In other aspects, means for reducing distortion is included such that the image distortion is less than about 2%. By way of example, the distortion reduction means can include edge lenslets having more or less power than other lenslets within the same array. These edge lenslets are adjacent to one or more edges of the magnifier so as to compensate for pincushion, barrel or petzval distortion, known to those in the art.
The invention also provides for certain improvements in a method of manufacturing a microlenslet array of the type having a plurality of lenslets formed within a optical substrate having a first planar surface, a second planar surface, and a normal vector that is substantially perpendicular to each surface. Specifically, the improvement of the invention includes the steps of forming a first lenslet array within the first surface, forming a second lenslet array within the second surface, forming a plurality of lenslet channels between the lenslet arrays wherein each channel includes one lenslet from each of the arrays, the lenslet channels between at least two adjacent arrays having a channel axis vector relative to the normal vector such that the cross product between the channel axis vector and the optical axis vector is greater for lenslet channels further away from a line extending along a center of the substrate and parallel to the normal vector.
In another aspect, a method of manufacturing a microlens stack is provided for producing a magnified image of an object along an optical axis, including the steps of: combining at least two refractive lenslet arrays with at least one diffractive lenslet array to form a lenslet array stack with a plurality of lenslet channels, each of the channels having a sloped axis between at least two of the arrays, and arranging the channels such that the cross product between the sloped axis and the optical axis is greater for lenslet channels further from the optical axis as compared to lenslet channels closer to the optical axis, thereby achieving the magnification selectively.
Such a method can include, in another aspect, the step of arranging the channels such that at least two channels contribute to the image of each point of the object, providing continuous imagery. The method can also include the step of arranging at least one array so as to produce an intermediate image of the object and between other arrays, and inserting a field stop at the intermediate image so as to reduce the field of view of at least one channel.
In still another aspect, a stacked array imaging system has an integral MEMS device, or other electromechanical or opto-electronic actuator device, in the construction between stacks to effect a variable spacing between stack elements. The MEMS or actuator increases or decreases, selectively, the space between lenslets along a channel so as to change the optical conjugates and thereby change the system magnification. The MEMS actuators also provide for an array of electronically adjustable aperture stops or irises. The adjustable array of irises modify the image properties to improve or modulate the Optical Transfer Function, to turn xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d select lenslet channels, or to otherwise modify the optical transform of the object space scene into image space as in optical signal processing for pattern recognition or encryption or decryption.
In still another aspect, a tiled array imager is provided for generating an image of an object along an optical axis between the object and the image. To form the tiled array, at least two stacks are arranged substantially perpendicular to the optical axis. Each of the stacks are formed of a plurality of lenslet arrays including one or more non-refractive lenslet arrays and one or more refractive lenslet arrays. Each lenslet array within a tiled array acts substantially in concert as a single lenslet array; and the tiled arrays form a plurality of lenslet channels. Each of the channels between at least two arrays has a channel axis with a predefined slope relative to the optical axis. The lenslet channels further from the optical axis have a larger slope than lenslet channels closer to the optical axis. These slopes providing demagnification between the object and the image.
The invention also provides for scene generating apparatus, including: a computer for generating signals representative of an selected pattern; a flat panel display responsive to the signals to display the pattern, the display having a display center and a normal vector perpendicular to a face of the display means; a plurality of lenslet arrays formed into a stack having a plurality of lenslet channels, the channels between at least two arrays having a sloped channel axis relative to the surface normal vector, the lenslet arrays being constructed and arranged to generate an image of the pattern on the display means, the cross product of the sloped channel axis and the surface normal vector being larger for channels further from the center as compared to channels closer to the center wherein selective magnification of the image is achieved.
In another aspect, a digital camera is provided, including: a film-formatted camera body and camera lens which generate an image of a scene at an image plane within the camera body and in a format corresponding to 35 mm film; one or more non-refractive lenslet arrays and one or more refractive lenslet arrays formed into a stack with a first outer surface and a second outer surface, the stack being constructed and arranged to fit with the camera body, the lenslet arrays forming a plurality of lenslet channels which act in concert to form a secondary image of the camera""s first image that is sized to a solid state focal plane array; and a solid state focal plane array arranged at the secondary image.
In yet another aspect, a digital camera is provided, including: a solid state imaging device of the type that includes an array of detector pixels responsive to electromagnetic radiation within a range of wavelengths; a window for protecting the device and for imaging the radiation onto the device, the window having one or more non-refractive lenslet arrays and one or more refractive lenslet arrays formed into a stack, the stack being constructed and arranged over the device and forming a plurality of lenslet channels which act in concert to form an image that is sized to the device.
The invention also provides a compact optical correlator for imaging an object to a solid state detector, including: a first stack and a second stack arranged substantially perpendicular to an axis formed between the object and the detector, each stack having one or more non-refractive lenslet arrays and one or more refractive lenslet arrays, the lenslet arrays forming a plurality of lenslet channels wherein each channel includes one lenslet from each of the other arrays, the first stack generating a Fourier image between the first and second stacks at a filtering plane, the second stack generating an image of the Fourier image such that the object is reimaged onto the detector; and an optical filter arranged at the filtering plane for selectively filtering electromagnetic energy so as to achieve selected optical processing.
In one aspect of the invention, a lenslet array stack is integrated with other like lenslet array stacks in a seamless tile so as to achieve a large format display. Each stack includes at least one refractive lenslet array and at least one non-refractive lenslet array. The stacks are abutted in a manner which achieves the size of the desired large format display; the abutted stacks thus functioning, substantially, as a single stack. At the point of intersection between adjacent stacks, the individual stacks provide substantially 100% fill factor; and thus the intersection is substantially unnoticeable.
By way of example, advancements in microelectronics manufacturing technology have recently produced miniature FPDs with relatively low cost, and high quality, resolution and yield. These miniature FPDs typically have pixel clear aperture sizes of about twenty-five microns and an overall dimension of 12.7 mm by 12.7 mm (standard LCD pixel sizes, by contrast, are typically about two hundred and fifty microns, or one hundred dots per inch). They are used, for example, within head-mounted displays for defense and commercial applications. The miniature FPDs offer high optical performance and good contrast with about twenty to forty lines-per-mm resolution. In accord with one aspect of the invention, an array of miniature FPDs are tiled into a larger FPD of selected size. One or more lenslet array stacks are thus arranged so as to reimage and magnify the tiled FPD into a large format display. In one practical aspect, the stacks too are tiled. Accordingly, the tiled stacks and the tiled miniature FPDs provide a convenient and efficient large format display of minimal thickness and with substantially seamless effects caused by the tiling. The FPD is thus scaleable, according to the invention, in a flexible, low cost, high performance assembly.
Lenslet array stacks of the invention can provide selective magnification, as discussed herein. Like magnification stacks can also be arranged, in sequence, to achieve integer multiple magnifications between an object and image. Accordingly, and in another aspect of the invention, one method of the invention is to provide a magnification of n*M, wherein n denotes the number of lenslet array stacks, and where M denotes the magnification of the stack in the sequence.
The lenslet arrays of the invention can be formed in optical grade polymer, fused silica, quartz, sapphire, calcium, fluoride, optical grade glass, silicon, germanium, gallium arsenic, silicon carbide, zinc sulfide, zinc selenide, and other glass or crystalline materials that transmit ultraviolet, visible or infrared light with low absorption and high efficiency. Certain polymers, gels and other organic materials can also be used, such as bacteriorhodopsin, as known to those skilled in the art.
The invention provides several advantages and has widely varying uses. It provides, for example, hybrid diffractive-refractive optical magnifiers for use in optical display and imaging systems, e.g., flat panel displays, classical cameras, and medical imagers. In one practical application, the invention has beneficial use in bridging 35 mm film technology to the digital age by conveniently reformatting the classical image plane to the industrial sizes of the modern day solid-state devices. In the realm of Fourier and/or digital systems, the invention further provides a convenient forum from which to implement a variety of optical correlation or processing techniques, including Fourier processing, optical computing, and data transmission methods. Certain other applications, aspects and advantages are realized by the invention, including:
(1) Hybrid lenslet arrays (i.e., lenslet arrays made from refractive lenslets and at least one array of non-refractive lenslets) of the invention can provide selective magnification of miniature flat panel electronic displays. These arrays form a system that exploits the advances made in microelectronic packaging and manufacturing so that high resolution active matrix displays are available at high yield and low cost. Such a system further enables a large visible field with a high fill factor (i.e., high throughput and xe2x80x9cframelessxe2x80x9d operation so that the joint between adjacent stacks in a tile are unnoticeable) and yet with low overall weight, size and complexity.
(2) Hybrid lenslet arrays according to the invention are generally scaleable such that stacks of adjacent arrays perform like functions so as to provide a combined effect with reduced overall manufacturing complexity. For example, a hybrid array with an achieved magnification of two hundred percent can be combined with a similar array to achieve an overall object-to-image magnification of four hundred percent. This obviously permits the simultaneous and simplified manufacture of like arrays along a common manufacturing line, which lowers cost and which increases production yield.
(3) Because of the high resolution and low weight provided by a system of the invention, hybrid arrays of the invention are particularly suited to avionic displays; optical systems at command and control centers; high definition television (HDTV); passenger, conference and stadium displays; virtual conference centers; and active billboards.
(4) A hybrid lenslet array forming a stack according to the invention preferably has precise registration along the individual lenslet channels defined by the stack transfer, transform or optical radiation transfer from object space to image space. This provides accuracy in characteristics of image quality, optical computing and processing.
(5) A stack of microlenslet arrays according to the invention can provide either magnification or demagnification for a variety of specific applications.
(6) A stack of microlenslet arrays with a MEMS actuator device according to the invention can provide electronic adjustment or tunable magnification for electronic imaging, display or other applications.
(7) Microlenslet surface structure, according to the invention, can be (a) refractive, (b) diffractive kineforms, (c) high order, high efficiency diffractive steering or focusing lenslets, (d) holograms or holographic lenslets, (e) computer generated holograms, (f) effective index modulating surface arrays, (g) apodizing or other spatial filters, and arrays of stops, or (h) other features typically generated by lithographic and semiconductor fabrication technology.
(8) In accord with the invention, hybrid lenslet arrays are formed into a stackxe2x80x94a process sometimes denoted herein as xe2x80x9chybridizationxe2x80x9dxe2x80x94of different surface types (refractive and diffractive in nature) to provide excellent color, aberration or other correction for high efficiency, high Modulation Transfer Function (MTF) and uniformity over a large aperture optical system.
(9) When combined with a mechanical support structure, the input and/or output surfaces of a stack provide a clear aperture which is at least equivalent to, or greater than, the mechanical aperture of the support structure. This permits seamless, or xe2x80x9cframeless,xe2x80x9d tiling of a plurality of stacks into an infinitely scaleable, tiled, massive parallel processed array for very large display or image acquisition over a large field of view. xe2x80x9cMassive parallel processing,xe2x80x9d as sometimes referred to herein, means the parallel addressing and control of solid state devices like the CCD and frame readout for the tiled imaging or FPD projection system constructed according to the invention. Massive parallel processing effects simultaneous activation or control of tile elements for real-time applications (i.e., many frames per second). By way of example, if control and readout electronics were serial, as opposed to parallel, then the screen or refresh rates can extend an unreasonable period of several minutes.
(10) Microlenslet fabrication of an array of stacks, e.g., to form a tile and/or to achieve integer and repeated magnification effects, permits the cost effective manufacture of large scale assemblies. By way of example, massive parallel processing of discrete tile subassemblies allows for cost effective computer control of large scale, seamlessly tiled array systems and at very large speeds such as real-time video rates or faster.
(11) A lenslet array, according to the invention, can include macroscopic planar or refractive lens surfaces in addition to the microlenslet surface structures. Such a lenslet array can provide macroscopic radiation transfer according to a first purpose, and lenslet channel radiation transfer according to a second purpose. In addition, a lenslet array of the invention can and usually does include interstitial planar microsurfaces, arranged between adjacent lenslets, that do not generally contribute to the overall optical throughput from the object to the image.
(12) In certain aspects of the invention, a stack of hybrid lenslet arrays are arranged to efficiently reimage a discrete pixelated object into a discrete pixelated image. Alternatively, such a stack can be arranged to image an object into a continuous imagexe2x80x94without dark spaces, gaps or blurred regions between adjacent pixels or local image areas at the image planexe2x80x94by careful image interlacing of adjacent channels or kernels of channels in the stacked array structure.
(13) Image interlacing of adjacent lenslet channels provides a uniform, high efficiency optical tile system with a total optical path length or working distance which scales with the size and f-number of the channels. This provides for a flat panel optical system with a thickness, weight and mass that is smaller than that which is typical for a conventional macroscopic lens or mirror optical system.
(14) The lenslet arrays of the invention can be represented by a uniform array of lenslets of equal surface figure at regular spaced intervals, or by kernels of subarray lenslets of equal surface figure at regular spaced intervals, or by uniquely different lenslets at regular or irregular spacing. In certain aspects the lenslet arrays can be formed of lenslets with varying distance from adjacent lenslets dependent upon a location from an optical or mechanical center of the lenslet array surface. In yet other aspects, the lenslet arrays are arranged in a radially symmetric fashion, in a manner easily defined by the Cartesian coordinate system, or in another group symmetry.
(15) The microlenslets of the invention can have circular, square, hexagonal or other regularly shaped apertures which are equal to or smaller to the lenslet-to-lenslet center spacing (i.e., so as to provide a zone, between lenslets, that does not transfer radiation along a lenslet channel). Nevertheless, lenslets are usually circular in shape.
(16) The microlenslets, the microlenslet surfaces, and/or the spaces between adjacent lenslets can contain hard stops, masks or opaque zones to achieve one or more of the following: to control crosstalk, to eliminate or reduce stray light, to reduce image artifacts and aberrations, to maximizing image contrast, and to optimize MTF. Intra-element stops or opaque zones can be fabricated by chemical modification of the lenslet array substrate material, by trench etching, and by thermal or other physical processing. Surface stops can be fabricated using physical deposition, chemical modification, printing or other process for depositing or placement of opaque material in the interstices between lenslets. Inter-element stops can include a metal or other opaque mask which also provides for accurate spacing and precision as to the location of adjacent arrays in the stack.
(17) The microlenslets and/or spaces between adjacent lenslets can contain adjustable actuator intra-element stops such as MEMS-type irises to achieve one or more of the following; to control crosstalk, to eliminate or reduce stray light, to reduce image artifacts and aberrations, to maximize image contrast, to improve image uniformity, to optimize MTF, and to adjust or tune the system f-stop.
(18) A hybrid lenslet stack of the invention provides magnification or demagnification, in one aspect, by outward or inward tilting of lenslets channels relative to an optical axis. In another aspect, the stack can also utilize microlenslet array channels to effect magnification or demagnification by outward or inward steering of individual lenslet channel axes. Further, magnification (or demagnification) can be divided equally or unequally between arrays within a stack, or between stacks arranged as a sequence of stacks in a single optical train. Furthermore, the magnification can be adjustable using a MEMS actuator device at a location between stacks. The MEMS actuator can be addressed electronically to increase or decrease the spacing between stacks in order to change the optical conjugates of the imaging system.
(19) In the case of pixelated objects or images, individual lenslet apertures can be smaller than, equal to, or larger than the pixelated dimensions of the object or image. Lenslet apertures which are larger than the pixel dimensions of the object or image can have (a) fields of view covering a plurality of the pixels in object or image space, or (b) a field of view which exceeds the aperture of the lenslet with potential overlap among the fields of view of multiple lenslet channels. Lenslets apertures that equal the pixelated dimensions in object space can (a) transfer the image of many object pixels or just one object pixel, or (b) have field of view equal to the lenslet aperture dimension. Lenslets with apertures that are smaller than the pixelated object and/or image dimensions can utilize or interlace the images of a plurality of lenslets so as to image one point in object space to one point in image space.
Lenslets which have an aperture that equals the field of view are the least preferred configuration due to the extremely tight tolerance required in fabrication, registration, and the low defect density required to achieve uniform image transfer. Lenslets with apertures that are larger than the lenslet""s field of view require simpler masks for fabrication with reduced features; but defect densities can not be tolerated unless multiple lenslet channels are used to image a single point in object space to image space. Lenslet arrays with small aperture sizes, relative to the lenslet""s field of view, require the most complicated masks for fabrication and the lowest packing fraction for optical efficiency; but also allow for the greatest tolerance in registration and defect density due to the interlacing of images from many channels from a single object point.
(20) Hybrid lenslet array stacks according to the invention can provide inverted or erect images. Systems with erect images require an odd number (i.e., 1, 3, 5 . . . or 2n+1, where n is an integer number) of field stops or field image surfaces internal to the stack structure. Systems with an inverted image output can have either zero or an even number of field stops or field image surfaces internal to the stack structure. Stacks with internal field images can incorporate field stops in the form of micromachined, electro-formed, molded or other aperture plates for aberration control or the improvement of image quality (e.g., MTF).
(21) Stacks constructed according to the invention generally include, at least, four lenslet array surfaces and two substrate elements. The stack can be assembled as a stack of discrete air-spaced elements with external mechanical fixturing or with mechanical spacers placed between the elements and arrays. Such a stack provides a stable, monolithic structure which easily integrates into a system, device or product.
Stack surfaces and/or spacers can include fiducial marks to facilitate micron-level registration and location of components. These fiducial marks can be deposited, or male or female patterns can be etched into, surfaces at interstices between microlenslets. The opposing surface or fiducial mark of the next element or spacer between elements can also have fiducial marks or a mating surface relief pattern to facilitate assembly and co-location of elements and components of the assembly.
Alternatively, the lenslet apertures can be register into one or more mask plates between adjacent elements of the stack to provide for co-location and precise positioning in x-, y- and z-axes of the hybrid stack. Monolithic, self-alignment construction of stack assemblies allows for compact, high performance optical systems with superior structural and environmental integrity in comparison to conventional optical systems. Stack optics can also be assembled with buried and cemented surfaces for added reliability and impermeability to contamination or dirt.
(22) Multi-element stack optical systems of the invention with one or more intermediate image planes facilitate the insertion of passive or active media at a field image or at a collimated space between two lenslets in the stack. Active media located at the field stop provides a convenient forum from which to accomplish optical processing, and can include: electro-optic modulators, liquid crystal light valves, active color filter mosaics, other spatial light modulators, computer generated holograms, and even gain media to accommodate a wide variety of applications for optical transform systems, compact optical correlators, optical network and computing systems, switching systems and numerous other optical signal processors. Fixed passive spatial filters, color filters, or encryption filters can also be co-located at a field image in the stack assembly to create a wide variety of fixed or passive optical signal processing systems. Again, the compact, monolithic nature of the stack assembly allows for ease of assembly and integration with internal devices, associated electronics and mechanical fixturing.
(23) Multi-element stack optical systems of the invention with one or more intermediate image planes facilitate the arrangement of a MEMS device or other actuator mechanism or array of actuators at a field image or in the space between two adjacent stacks. The actuators can be in the form of an array of moveable irises or shutters in the path of the optical channels. The irises or shutter mechanisms can be used to effect an analog or digital transformation of the optical signal as in an optical signal processor or encryption/decryption system.
(24) Stack components and assemblies can be fabricated using a wide variety of materials and methods compatible with volume microelectronics assembly tooling and equipment. Substrates can be semiconductor, glass, single crystal, polycrystalline, liquid crystal, polymer or other optically transmissive material amenable to processing into microlenslet arrays. Metal or other solid negative masters can be used for mold fabrication of hybrid lenslet arrays and stacks. Hybrid arrays can also be cemented to bury surfaces for added reliability. Spacers between elements can be glass, metal, polymer, crystalline or other appropriate structural or optically opaque medium to facilitate registration and to enhance optical and mechanical properties. Active and passive devices located between elements, particularly at field image planes, can further incorporate electronics and mechanics for assembly and fixturing of stacks and lenslet arrays.
(25) Stacks and lenslet arrays of the invention can apply to applications across the optical spectrum, from the deep ultraviolet to the far infrared. Indeed, many semiconductor materials that facilitate microelectronic fabrication processing have excellent infrared transmission properties so as to support infrared applications. The compact, flat panel nature of the stack optical system allows for easy integration with an image plane device such as a focal plane array detector. The stack optics can also function as an optical signal processing window which isolates and protects the FPA device in a protective atmosphere, or in a controlled environment atmosphere such as cryogenic or other thermally controlled environment (e.g., heated, isothermal, and non-cryogenic-cooled).
(26) The stack assembly, according to the invention, provides a single optical assembly for use in imaging, display or detection applications using a single flat panel display, focal plane array, other direct display device or detector device. The ability to fabricate stack optics with nearly 100% clear aperture (relative to the mechanical size of the stack) allows for infinitely scaleable tiling of massive parallel processed arrays for very large flat panel displays or wide area, high resolution image acquisition systems.
(27) In addition to the applications discussed herein, the invention is particularly well suited for application with (a) massively parallel processed tiled large area FPD systems, (b) massively parallel processed large area real-time medical imaging systems, (c) compact optical correlators, (d) compact IR FPA imaging cameras with an integral cold stop, (e) compact CCD imaging systems, and (f) optical encryption systems for security applications.
The fabrication of a stack or SAM assembly according to the invention has many aspects, including:
(28) The lenslet arrays of the invention can be manufactured by molding an optical grade polymer, or by coextrusion of an optical polymer, with an opaque polymer. In one aspect, the mold is fabricated from a negative relief of the refractive and non-refractive lenslet surface features, plus fiducial marks and mechanical assembly features. The negative relief is then fabricated into a metal, ceramic or high temperature composite master, which is produced by micromachining or by direct forming into the master mold material. In another aspect, the mold is produced in an iterative manner by transferring a positive master in glass, semiconductor or crystal material to a ceramic or elastomer template, which creates the negative mold master.
(29) The arrays of the invention are made from a variety of substrate materials. Depending upon the wavelengths of operation, the substrates within a particular stack can be made from one or more different substrate materials so as to correct for optical color or to accomplish different distributions of optical power within the stack.
(30) Lenslet arrays of the invention can also be manufactured through replication. In this aspect, a mold is fabricated from a negative relief of the refractive and non-refractive lenslet microsurface features, as well as of the fiducial and mechanical assembly features. Preferably, the negative relief is fabricated into a metal, ceramic or high temperature composite master, which is produced by micromachining or by direct forming into the master mold material. The master is thereafter coated with a release agent followed, for example, by (a) an epoxy, (b) a polymer, (c) an optical quality organic, or (d) a sol gel material to produce a thin sheet of material with lenslet array features, fiducial marks, and mechanical assembly features to facilitate transfer and bonding to a flat optical substrate. The bulk optical substrate can additionally include opaque interstitial areas or masks to provide for stops and to eliminate or reduce optical crosstalk among nearby lenslet channels.
(31) Fabrication of lenslet arrays according to the invention can beneficially utilize substrates, equipment and process technology common to semiconductor microelectronic lithography. These semiconductor processes can include deposition and photoresist mask generation to facilitate the fabrication of surface features, the modification of the index of refraction, and the application of physical masks. Reactor processes common to semiconductor processing are also used, in other aspects, for chemical etching, reactive ion etching, plasma etching, physical vapor deposition, chemical vapor deposition, epitaxial growth, ion implantation, electron beam deposition, and other radiation exposure and activation processes to form refractive and non-refractive lenslet arrays with the selected substrate material.
(32) The interstitial regions between lenslet channels are preferably coated with an opaque materialxe2x80x94such as metal, ceramic or oxidexe2x80x94using semiconductor microelectronic processes, particularly the reversal of the photomask resist process described above.
(33) In a preferred aspect of the invention, the masks used to fabricate the lenslet arrays include fiducial features, which facilitate alignment and registration of lenslet array channels in cartesian x-y and rotational coordinates. The fiducials are either located outside of the lenslet clear aperture or interstitial to the lenslet array features. These fiducials can be clear with an opaque background, or opaque in a transparent background.
(34) The fiducial features of the invention can frame the entire lenslet array mask, or parts of the lenslet array mask, or within interstitial regions to the lenslet array channels. Fiducials can be horizontal or vertical lines, sequences of lines, crossed lines, circles, squares, hexagons, other geometries or combinations of geometric shapes.
(35) Generally, the fiducial markings facilitate the manufacture of precise registration of photomasks and lenslet stacks by co-alignment and/or registration. The markings can also create optical effects to assist in this assembly process. For example, precise alignment of the marks within a substrate and relative to a side-to-side arrangement of arrays can be made to produce optical effects such as a Moire pattern or other interference effect so as to indicate proper registration.
(36) In a preferred aspect of the invention, lenslet array substrates are fabricated with additional fiducial marks, or surface relief features (etched below the surface or protruding above the plane of the lenslets) to facilitate stack assembly. In particular, these fiducials can be used to assist in the alignment of elements such as mechanical spacers between adjacent arrays, or in the positioning of stops or optoelectronic devices at an intermediate image plane. Their placement can be outside, or interstitial to, the array""s clear aperture; and their shape can be in the form of lines, crosses, dots, rectangles, squares or other geometric features that permits visual or machine-aided alignment of stack elements. The fiducials can further facilitate mechanical pinning or interlocking of adjacent stack elements.
(37) In one convenient aspect of the invention, fiducial marks and assembly features are fabricated of metal or other target materials used in the masking of the interstitial and surrounding regions of the lenslets. In another aspect, the fiducial marks and assembly features are etched into the substrate. In yet another aspect, the fiducial marks and assembly features are fabricated onto mechanical spacers and other devices for placement within the stack.
(38) Fiducial marks and assembly features can be formed of solder, thermoset or other material that transforms from a solid to a liquid when subjected to heat or other activation such that a surface tension is created to promote alignment of the stack. The subsequent transformation of the fiducial and assembly features back to a solid thereby bonds the stack together into a monolithic structure.
(39) The stack can include lenslet surfaces that are immersed in an adhesive for monolithic bonding of the SAM.
(40) Stack assembly with micromechanical and electronic parts is greatly facilitated by visual or machine-aided tooling such as a microscope or other imaging devices. Typically, these devices have sufficient magnification to view the fiducial alignment microfeatures so as to facilitate precise array positioning in x, y and rotational coordinates.
(41) In another aspect, anaerobic, thermoset, room temperature adhesives or other bonding agents are used to assemble the stacks at the edges or at internal locations within the stack.
(42) Mechanical spacers and surface alignment features can include a gel, thermoset or a solder which bonds the stack together when activated at the point of proper registration.
(43) Stack alignment features can include thru-holesxe2x80x94at the edge of the stack""s clear aperture or at interstitial locations relative to the lenslet channelsxe2x80x94so as to provide for the insertion of micromechanical pins which assist stack assembly and which mechanically tie the stack into a monolithic structure.
(44) A substrate can include features which are designed into its outer surfaces to facilitate the assembly of the SAM relative to external mechanical mounts or housing structure. Further, such features can assist in the alignment and placement of an array relative to an imaging device, detector, or display device, e.g., a LCD. They can also facilitate assembly of a seamless tiled array construction of SAMs into a massive parallel processing system.
In another aspect, the invention also concerns a hybrid, refractive/diffractive, stacked optical lens array imaging system that transmit a two-dimensional image from an object plane to an image plane. Specifically, the imaging system utilizes a stack of arrays of lenses, each array comprising a plurality of small apertured lenses (xe2x80x9cmicrolensesxe2x80x9d or xe2x80x9clensletsxe2x80x9d). The optical imaging system includes micro-optics with a relatively short focal length and high optical efficiency and high resolution for imaging with or without magnification or demagnification. The optics thus form a xe2x80x9cstackxe2x80x9d of a plurality of hybrid (i.e., refractive, diffractive, etc.) lenslet arrays.
The system can provide for finite conjugate imaging or infinite conjugate imaging, and can contain at least one or more intermediate field images with an erect or inverted image at the overall system output image plane. The system can further reimage a pixelated object space to a discrete array image space. The system can also reimage a continuous object to a continuous image without dark spaces, gaps or blurred regions between pixels or image areas at the image plane.
Furthermore, the optical conjugates and continuous or discrete imaging properties of the system can be fixed or adjustable. Placement of one or more MEMS devices or other electromechanical actuators between lenslet stacks provides for increasing or modulating the spacing between stacks to effect a change in optical conjugates for the system. Alternatively, an array of MEMS irises or shutter devices can adjust the uniformity or continuity of a continuous or pixelated image.
Each array of lenslets may incorporate integral hard stops (such as chrome baffles) or opaque zones between lenslets for control of crosstalk, for minimization of stray light, and for maximization of image contrast and the modulation transfer function. A key aspect of the system is the interlacing of images from adjacent lenslet channels so that multiple lenslet channels may contribute to reimaging a point or pixel in object space to a corresponding point or pixel in image space. The effective f-number of the system is therefore smaller than the f-number of a single lenslet channel. The thickness of the system is a function of lenslet size, f-number and optical lens material, and is, therefore, substantially thinner than an equivalent optical system using large aperture macrolenses.
The stack of lenslet arrays can be configured and assembled within a monolithic structure for simplicity of construction and alignment. The image interlacing property of the system accommodates a large tolerance for lateral misalignment due to the contribution of multiple lenslet channels to the complete, continuous image.
The number of lenslets in each array stack can be greater than, equal to, or less than the total number of pixels in object or image space. Magnification can be divided equally among the lenslets or in various portions between the optical stack before and after the field stop array. Individual lenslets or entire lenslet arrays can be tilted inward or outward for magnification or demagnification. Lenslet arrays can be formed on planar substrates or can be hybridized with macrolens substrates. The lenslet surface figures can be constant over one array surface with uniform spacing. In the alternative, the surface figures can be arranged in kernels of n by m lenslets of constant figure or with changing figure in the adjacent kernels of lenslets. Or, the surface figures can vary step-wise across the entire aperture of the stack such that every lenslet has a unique figure unto itself.
The field stop array can incorporate either an array of reticles, a spatial light modulator, a MEMS actuator, other electromechanical actuator mechanisms, or other passive or active optical systems or media. The lenslets can be refractive, diffractive, holographically generated, or gradient indexed. The value of hybrid lenslet arrays is for chromatic correction, aberration correction or possible encryption to produce a desired corrected or processed image at the image plane.
The excellent uniformity of optical throughput and image quality across the entire clear aperture of the system at the image plane output allows for fabrication of xe2x80x9ctilesxe2x80x9d of the stacks with optics to the edge for 100% clear aperture. The tiles can be integrated into a very large, infinitely scaleable imaging or display system in a seamless fashion. For example, in one aspect, a large, high resolution, flat panel electronic wall display is formed using a plurality of small liquid crystal displays (xe2x80x9cLCDsxe2x80x9d), miniature flat panel displays (xe2x80x9cFPDsxe2x80x9d) or other compact displays, magnified and imaged through a mosaic array of tiles. In another example, an ultra-high resolution, large area, charge coupled device (xe2x80x9cCCDxe2x80x9d) medical X-ray imaging system is formed by tiling stacks with X-ray phosphor screen inputs to small, low-cost, high-speed CCD camera outputs. Massive parallel processors (xe2x80x9cMPPsxe2x80x9d) integrated within a high speed computer system permit video rate, real-time, or other high frame and data rate transfer of an image in the case of the medical X-ray system, or active display in the case of the wall display.
The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention.